The voltage of a distribution system is controlled by a tap change of a transformer (on-load tap-changing transformer LRT: Load Ratio Control Transformer) installed in a distribution substation or a tap change of an automatic voltage regulator (SVR: Step Voltage Regulator) installed on a distribution line. The on-load tap-changing transformers LRT and the automatic voltage regulators SVR adjust voltage by a machine mechanism (tap). The transformers and regulators will be hereafter collectively designated as voltage adjustment devices SVR.
These voltage adjustment devices SVR are generally so set that the devices operate with a response time constant of several tens of seconds before a tap change. When a plurality of voltage adjustment devices are installed in series in a distribution line, the response time constant of a voltage adjustment device installed on the end side of the distribution line (feeder) is generally slower than the response time constant of a voltage adjustment device installed on the substation side (sending side). Unnecessary operations of the voltage adjustment device on the end side are thereby reduced.
In recent distribution systems, the number of customers equipped with a solar power generation device has been increased. In this case, the power output of each solar power generation device depends on the weather fluctuation and is a cause of abrupt voltage fluctuation in distribution systems.
Meanwhile, suppression of abrupt voltage fluctuation is expected by connecting to a distribution system a SVC (static var compensator) or a STATCOM (static synchronous compensator) having a function of suppressing the voltage fluctuation by high-speed reactive power output control. The SVC and the STATCOM carry out reactive power compensation by a static mechanism (such as IGBT). These compensators will be hereafter collectively designated as static var compensator SVC.
When a voltage adjustment device SVR and a static var compensator SVC are installed in a distribution system, the voltage adjustment device SVR including a machine mechanism is installed on the substation side (sending side) and the static var compensator SVC operated with a static mechanism is installed on the end side of the distribution line (feeder). This arrangement is against the idea of conventional time coordinated control that a slower response time constant is set closer to the end of the feeder.
For this reason, when a voltage adjustment device SVR and a static var compensator SVC are installed together in a distribution system, the static var compensator SVC operates ahead of the voltage adjustment device SVR for the voltage fluctuation and steady voltage fluctuation is also suppressed by the static var compensator SVC. This may cause a phenomenon that the voltage adjustment device SVR will not operate.
In these cases, the static var compensator SVC continuously operates with the maximum output and lacks an output margin for suppressing abrupt voltage fluctuation. As a result, abrupt voltage fluctuation may not be suppressed. That is, there is a possibility that the function of suppressing voltage fluctuation against abrupt changes in photovoltaic power generation output, which is the intended purpose of the installation of the static var compensator SVC, cannot be performed.
When a voltage adjustment device SVR and a static var compensator SVC are installed together, it is important for both to appropriately exercise the suppression control of the voltage fluctuation.
Various techniques have been disclosed as control methods for operating a voltage adjustment device SVR and a static var compensator SVC in a coordinated manner. For example, Document 1 discloses a method that, in an optimum voltage adjustment device, the amounts of control of a voltage adjustment device SVR and a static var compensator SVC are determined by solving an optimization problem and the amounts of control are taken as a control command values for the individual devices.
Document 2 discloses a method of reducing the reactive power output of a static var compensator SVC with time and thereby transferring a control to a voltage adjustment device SVR and to share the control.